Utilizing venting in a MEMS liquid pumping system

ABSTRACT

The venting of an ink jet nozzle arrangement is achieved by providing an air inlet in fluid communication with a hydrophobic surface of a thermal actuator. The air inlet allows the flow of air into and out of a volume adjacent the hydrophobic surface. The air inlet can also be defined by a number of small spaced apart holes formed in a hydrophobic material.

CROSS REFERENCES TO RELATED APPLICATIONS

The following Australian provisional patent applications are hereby incorporated by cross-reference. For the purposes of location and identification, U.S. patent applications identified by their U.S. patent application serial numbers (U.S. Ser. No.) are listed alongside the Australian applications from which the U.S. patent applications claim the right of priority.

CROSS-REFERENCED U.S. PATENT/ AUSTRALIAN PATENT APPLICATION PROVISIONAL (CLAIMING RIGHT OF PATENT PRIORITY FROM AUSTRALIAN DOCKET APPLICATION NO. PROVISIONAL APPLICATION) NO. PO7991 09/113,060 ART01 PO8505 09/113,070 ART02 PO7988 09/113,073 ART03 PO9395 09/112,748 ART04 PO8017 09/112,747 ART06 PO8014 09/112,776 ART07 PO8025 09/112,750 ART08 PO8032 09/112,746 ART09 PO7999 09/112,743 ART10 PO7998 09/112,742 ART11 PO8031 09/112,741 ART12 PO8030 09/112,740 ART13 PO7997 09/112,739 ART15 PO7979 09/113,053 ART16 PO8015 09/112,738 ART17 PO7978 09/113,067 ART18 PO7982 09/113,063 ART19 PO7989 09/113,069 ART20 PO8019 09/112,744 ART21 PO7980 69/113,058 ART22 PO8018 09/112,777 ART24 PO7938 09/113,224 ART25 PO8016 09/112,804 ART26 PO8024 09/112,805 ART27 PO7940 09/113,072 ART28 PO7939 09/112,785 ART29 PO8501 09/112,797 ART30 PO8500 09/112,796 ART31 PO7987 09/113,071 ART32 PO8022 09/112,824 ART33 PO8497 09/113,090 ART34 PO8020 09/112,823 ART38 PO8023 09/113,222 ART39 PO8504 09/112,786 ART42 PO8000 09/113,051 ART43 PO7977 09/112,782 ART44 PO7934 09/113,056 ART45 PO7990 09/113,059 ART46 PO8499 09/113,091 ART47 PO8502 09/112,753 ART48 PO7981 09/113,055 ART50 PO7986 09/113,057 ART51 PO7983 09/113,054 ART52 PO8026 09/112,752 ART53 PO8027 09/112,759 ART54 PO8028 09/112,757 ART56 PO9394 09/112,758 ART57 PO9396 09/113,107 ART58 PO9397 09/112,829 ART59 PO9398 09/112,792 ART60 PO9399 6,106,147 ART61 PO9400 09/112,790 ART62 PO9401 09/112,789 ART63 PO9402 09/112,788 ART64 PO9403 09/112,795 ART65 PO9405 09/112,749 ART66 PP0959 09/112,784 ART68 PP1397 09/112,783 ART69 PP2370 09/112,781 DOT01 PP2371 09/113,052 DOT02 PO8003 09/112,834 Fluid01 PO8005 09/113,103 Fluid02 PO9404 09/113,101 Fluid03 PO8066 09/112,751 IJ01 PO8072 09/112,787 IJ02 PO8040 09/112,802 IJ03 PO8071 09/112,803 IJ04 PO8047 09/113,097 IJ05 PO8035 09/113,099 IJ06 PO8044 09/113,084 IJ07 PO8063 09/113,066 IJ08 PO8057 09/112,778 IJ09 PO8056 09/112,779 IJ10 PO8069 09/113,077 IJ11 PO8049 09/113,061 IJ12 PO8036 09/112,818 IJ13 PO8048 09/112,816 IJ14 PO8070 09/112,772 IJ15 PO8067 09/112,819 IJ16 PO8001 09/112,815 IJ17 PO8038 09/113,096 IJ18 PO8033 09/113,068 IJ19 PO8002 09/113,095 IJ20 PO8068 09/112,808 IJ21 PO8062 09/112,809 IJ22 PO8034 09/112,780 IJ23 PO8039 09/113,083 IJ24 PO8041 09/113,121 IJ25 PO8004 09/113,122 IJ26 PO8037 09/112,793 IJ27 PO8043 09/112,794 IJ28 PO8042 09/113,128 IJ29 PO8064 09/113,127 IJ30 PO9389 09/112,756 IJ31 PO9391 09/112,755 IJ32 PP0888 09/112,754 IJ33 PP0891 09/112,811 IJ34 PP0890 09/112,812 IJ35 PP0873 09/112,813 IJ36 PP0993 09/112,814 IJ37 PP0890 09/112,764 IJ38 PP1398 09/112,765 IJ39 PP2592 09/112,767 IJ40 PP2593 09/112,768 IJ41 PP3991 09/112,807 IJ42 PP3987 09/112,806 IJ43 PP3985 09/112,820 IJ44 PP3983 09/112,821 IJ45 PO7935 09/112,822 IJM01 PO7936 09/112,825 IJM02 PO7937 09/112,826 IJM03 PO8061 09/112,827 IJM04 PO8054 09/112,828 IJM05 PO8065 6,071,750 IJM06 PO8055 09/113,108 IJM07 PO8053 09/113,109 IJM08 PO8078 09/113,123 IJM09 PO7933 09/113,114 IJM10 PO7950 09/113,115 IJM11 PO7949 09/113,129 IJM12 PO8060 09/113,124 IJM13 PO8059 09/113,125 IJM14 PO8073 09/113,126 IJM15 PO8076 09/113,119 IJM16 PO8075 09/113,120 IJM17 PO8079 09/113,221 IJM18 PO8050 09/113,116 IJM19 PO8052 09/113,118 IJM20 PO7948 09/113,117 IJM21 PO7951 09/113,113 IJM22 PO8074 09/113,130 IJM23 PO7941 09/113,110 IJM24 PO8077 09/113,112 IJM25 PO8058 09/113,087 IJM26 PO8051 09/113,074 IJM27 PO8045 6,111,754 IJM28 PO7952 09/113,088 IJM29 PO8046 09/112,771 IJM30 PO9390 09/112,769 IJM31 PO9392 09/112,770 IJM32 PP0889 09/112,798 IJM35 PP0887 09/112,801 IJM36 PP0882 09/112,800 IJM37 PP0874 09/112,799 IJM38 PP1396 09/113,098 IJM39 PP3989 09/112,833 IJM40 PP2591 09/112,832 1JM41 PP3990 09/112,831 IJM42 PP3986 09/112,830 IJM43 PP3984 09/112,836 IJM44 PP3982 09/112,835 IJM45 PP0895 09/113,102 IR01 PP0870 09/113,106 IR02 PP0869 09/113,105 IR04 PP0887 09/113,104 IR05 PP0885 09/112,810 IR06 PP0884 09/112,766 IR10 PP0886 09/113,085 IR12 PP0871 09/113,086 IR13 PP0876 09/113,094 IR14 PP0877 09/112,760 IR16 PP0878 09/112,773 IR17 PP0879 09/112,774 IR18 PP0883 09/112,775 IR19 PP0880 6,152,619 IR20 PP0881 09/113,092 IR21 PO8006 6,087,638 MEMS02 PO8007 09/113,093 MEMS03 PO8008 09/113,062 MEMS04 PO8010 6,041,600 MEMS05 PO8011 09/113,082 MEMS06 PO7947 6,067,797 MEMS07 PO7944 09/113,080 MEMS09 PO7946 6,044,646 MEMS10 PO9393 09/113,065 MEMS11 PP0875 09/113,078 MEMS12 PP0894 09/113,075 MEMS13

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates to the venting of an ink jet nozzle.

BACKGROUND OF THE INVENTION

Recently, micro-electro mechanical systems (MEMS) have become increasingly popular. One use of such a system is in the ejection of ink in an ink jet printing device. It is important in such devices to have efficient operation.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an efficient operation of an ink jet nozzle when constructed on a MEMS scale.

In accordance with a first aspect of the present invention there is provided a micro-mechanical nozzle having thermal actuator which includes a hydrophobic surface surrounded by other hydrophobic surfaces. A method of reducing the operation energy requirements of said actuator comprises the step of providing an air inlet in fluid communication with said hydrophobic surface. The air inlet allow the flow of air into and out of a volume adjacent said hydrophobic surface. Further, the air inlet is surrounded by hydrophobic material and includes a plurality of small spaced apart holes.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic cross-sectional view of a single ink jet nozzle incorporating a venting arrangement constructed in accordance with the preferred embodiment.

FIG. 2 is a schematic cross-sectional view of the single ink jet nozzle with a thermal actuator of the nozzle in its activated state.

FIG. 3 is a schematic diagram of a conductive layer utilized in the thermal actuator of the ink jet nozzle.

FIG. 4 is a close-up perspective view of portion A of FIG. 3.

FIG. 5 is a cross-sectional schematic diagram illustrating the construction of the conductive layer of FIG. 3.

FIG. 6 is a schematic cross-sectional diagram illustrating the development of a resist material through a half-toned mask utilized in the fabrication of the conductive layer of FIG. 3.

FIG. 7 is an exploded perspective view of the ink jet nozzle of FIG. 1.

FIG. 8 is a perspective view of a section of an ink jet printhead incorporating a plurality of the ink jet nozzles of FIG. 1.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

The preferred embodiment of the present invention will be discussed with reference to an ink jet nozzle wherein it is required to provide energy efficient operation of an ink jet printing device incorporating a plurality of the ink jet nozzles. The present invention should however, not be restricted to the field of ink jet printing devices.

In the preferred embodiment, the ink jet nozzle from which ink is ejected is actuated by means of a thermal actuator which includes a “corrugated” copper heating element encased in a polytetrafluoroethylene (PTFE) layer. Those of ordinary skill in the field will appreciate that PTFE is inherently hydrophobic.

Turning now to FIG. 1, there is illustrated a cross-sectional view of a single ink jet nozzle 10 in accordance with the present embodiment. The ink jet nozzle 10 includes an ink ejection port 11 for the ejection of ink from a chamber 12 by means of actuation of a thermal paddle actuator 13. The thermal paddle actuator 13 comprises an inner copper heating portion 14 and paddle 15 which are encased in a PTFE layer 16. The PTFE layer 16 has an extremely high coefficient of thermal expansion (approximately 770×10−6, or around 380 times that of silicon). The PTFE layer 16 is also highly hydrophobic which results in an air bubble 17 being formed under the actuator 13 due to out-gassing etc. A top surface of the PTFE layer 16 is treated so as to make it hydrophilic. The heating portion 14 is also formed within a lower portion of the actuator 13.

The heating portion 14 is connected at ends 20,21 (see also FIG. 7) to a lower CMOS drive layer 18 containing drive circuitry (not shown). For the purposes of actuation of the actuator 13, a current is passed through the heating portion 14 which heats the lower portion of the actuator 13. Turning now to FIG. 2, a bottom surface of the actuator 13, in contact with an air bubble 17 remains heated while any top surface heating is carried away by the exposure of the top surface of the actuator 13 to the ink within the chamber 12. Hence, the lower portion of the PTFE layer expands more rapidly resulting in a general bending upwards of the actuator 13 (as illustrated in FIG. 2) which consequentially causes the ejection of ink from the ink ejection port 11. An air inlet channel 28 is formed between a nitride layer 42, and a PTFE layer 26 such that air is free to flow in the direction of an arrow 29 along a channel 28 and through holes 25, to accommodate any fluctuating pressure influences plurality of posts 27 are positioned between the layers 42, 26. As can be seen in FIGS. 1 and 2, air introduced into the ink jet nozzle 10 is in fluid communication with the air bubble 17. Thus the air flow acts to reduce a vacuum acting on the bottom surface of the actuator 13 during operation. As a result, less energy is required for the movement of the actuator 13.

The actuator 13 can be deactivated by turning off the current to the heating portion 14. This results in a return of the actuator 13 to its rest position.

The actuator 13 includes a number of significant features. In FIG. 3 there is illustrated a schematic diagram of the conductive layer of the thermal actuator 13. The conductive layer includes the panel 15, which can be constructed from the same material as the heating portion as 14, i.e. copper, and which contains a series of holes 23. The holes 23 are provided for interconnecting PTFE both above and below the panel 15 so as to resist any movement of the PTFE layers past the panel 15 and thereby reduce any opportunities for the delamination of the PTFE and the copper.

Turning to FIG. 4, there is illustrated a close up view of a portion of the actuator 13 of FIG. 1 illustrating corrugations 22 of the heating portion 14. The corrugations 22 of the heater 14 allow for a rapid heating of the lower portion. Any resistive heater which is based upon applying a current to heat an object will result in a rapid, substantially uniform elevation in temperature of the outer surface of the current carrying conductor. The surrounding PTFE is therefore heated by means of thermal conduction from the resistive element. This thermal conduction is known to proceed, to a first approximation, at a substantially linear rate with respect to distance from a resistive element. By utilizing a corrugated resistive element, the lower portion of the actuator 13 is more rapidly heated. Therefore, the utilization of a corrugated resistive element results in a more rapid heating of the lower portion and therefore a rapid actuation of the actuator 13. Further the corrugations 22 also assist in resisting any delamination of the copper and PTFE.

Turning now to FIG. 5, the corrugations 22 can be formed by depositing a resist layer 50 on top of the first PTFE layer 51. The resist layer 50 is exposed utilizing a mask 52 having a half-tone pattern delineating the corrugations. After development, the resist layer 50 contains the corrugation pattern. The resist layer 50 and the PTFE layer 51 are then etched utilizing an etchant that erodes the resist layer 50 at substantially the same rate as the PTFE layer 51. This transfers the corrugated pattern into the PTFE layer 51. Turning to FIG. 6, on top of the corrugated PTFE layer 51 is deposited the heating portion 14 which takes on a corrugated form in accordance with its under layer. The copper heating portion 14 is then etched in a serpentine or concertina form. Subsequently, a second PTFE layer 53 is deposited on top of the heating portion 14 so as to form a top layer of the thermal actuator 13. Finally, the second PTFE layer 52 is planarized to form the top surface of the thermal actuator 13 (FIG. 1).

Returning again now to FIG. 1, it is noted that ink can be supplied via a channel 38 which can be constructed by means of deep anisotropic silicon trench etching such as that available from STS Limited (“Advanced Silicon Etching Using High Density Plasmas” by J. K. Bhardwaj, H. Ashraf, page 224 of Volume 2639 of the SPIE Proceedings in Micro Machining and Micro Fabrication Process Technology). The ink supply flows from the channel 38 through side grill portions 40 (see also FIG. 7) into the chamber 12. Importantly, the grill portions 40 which can comprise silicon nitride or similar insulating material act to remove foreign bodies from the ink flow. The grill 40 also helps to pinch the PTFE actuator 13 to a base CMOS layer 18, the pinching providing an important assistance for the thermal actuator 13 so as to ensure a substantially decreased likelihood of the thermal actuator layer 13 separating from a base CMOS layer 18.

A series of sacrificial etchant holes 19, are provided in a top wall 48 of the chamber 12 to allow sacrificial etchant to enter the chamber 12 during fabrication so as to increase the rate of etching. The small size of the holes 19, does not affect the operation of the device 10 substantially as the surface tension across the holes 19, stops ink from being ejected from these holes, whereas, the larger size port 11 allows for the ejection of ink.

Turning now to FIG. 7, there is illustrated an exploded perspective view of a single nozzle 10. The nozzle 10 can be formed in layers starting with a silicon wafer device 41 having a CMOS layer 18 on top thereof as required. The CMOS layer 18 provides the various drive circuitry for driving the copper heating portion 14.

On top of the CMOS layer 18 a nitride layer 42 is deposited, providing protection for lower layers from corrosion or etching. Next, a PTFE layer 26 is constructed having the aforementioned holes 25, and posts 27. The structure of the PTFE layer 26 can be formed by first laying down a sacrificial glass layer (not shown) onto which the PTFE layer 26 is deposited. The PTFE layer 26 includes various features, for example, a lower ridge portion 30 in addition to vias for subsequent material layers.

In construction of the actuator 13 (FIG. 1), the process of creating a first PTFE layer proceeds by laying down a sacrificial layer on top of layer 26 in which the air bubble underneath actuator 13 (FIG. 1) subsequently forms. On top of this is formed a first PTFE layer utilizing the relevant mask. Preferably, the PTFE layer includes vias for the subsequent copper interconnections. Next, a copper layer 43 is deposited on top of the first PTFE layer and a second PTFE layer is deposited on top of the copper layer 43, in each case, utilizing the required mask.

The nitride layer 46 can be formed by the utilization of a sacrificial glass layer which is masked and etched as required to form the side walls and the grill 40. Subsequently, the top nitride layer 48 is deposited again utilizing the appropriate mask having the holes 19 as required. Subsequently, the various sacrificial layers can be etched away so as to release the structure of the thermal actuator 13.

In FIG. 8 there is illustrated a section of an ink jet printhead configuration 90 utilizing ink jet nozzles constructed in accordance with the preferred embodiment, e.g. 91. The configuration 90 can be utilized in a three color process 1600 dpi print-head utilizing 3 sets of 2 rows of nozzle chambers 92,93, which are interconnected to one ink supply channel, e.g. 94, for each set. The 3 supply channels 94, 95, 96 are interconnected to cyan coloured, magenta coloured and yellow coloured ink reservoirs respectively.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiment without departing from the spirit or scope of the invention as broadly described. The present embodiment is, therefore, to be considered in all respects to be illustrative and not restrictive.

Ink Jet Technologies

The embodiments of the invention use an ink jet printer type device. Of course many different devices could be used. However presently popular ink jet printing technologies are unlikely to be suitable.

The most significant problem with thermal ink jet is power consumption. This is approximately 100 times that required for high speed, and stems from the energy-inefficient means of drop ejection. This involves the rapid boiling of water to produce a vapor bubble which expels the ink. Water has a very high heat capacity, and must be superheated in thermal ink jet applications. This leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.

The most significant problem with piezoelectric ink jet is size and cost. Piezoelectric crystals have a very small deflection at reasonable drive voltages, and therefore require a large area for each nozzle. Also, each piezoelectric actuator must be connected to its drive circuit on a separate substrate. This is not a significant problem at the current limit of around 300 nozzles per printhead, but is a major impediment to the fabrication of pagewidth printheads with 19,200 nozzles.

Ideally, the ink jet technologies used meet the stringent requirements of in-camera digital color printing and other high quality, high speed, low cost printing applications. To meet the requirements of digital photography, new ink jet technologies have been created. The target features include:

low power (less than 10 Watts)

high resolution capability (1,600 dpi or more)

photographic quality output

low manufacturing cost

small size (pagewidth times minimum cross section)

high speed (<2 seconds per page).

All of these features can be met or exceeded by the ink jet systems described below with differing levels of difficulty. Forty-five different ink jet technologies have been developed by the Assignee to give a wide range of choices for high volume manufacture. These technologies form part of separate applications assigned to the present Assignee as set out in the table under the heading Cross References to Related Applications.

The ink jet designs shown here are suitable for a wide range of digital printing systems, from battery powered one-time use digital cameras, through to desktop and network printers, and through to commercial printing systems.

For ease of manufacture using standard process equipment, the printhead is designed to be a monolithic 0.5 micron CMOS chip with MEMS post processing. For color photographic applications, the printhead is 100 mm long, with a width which depends upon the ink jet type. The smallest printhead designed is IJ38, which is 0.35 mm wide, giving a chip area of 35 square mm. The printheads each contain 19,200 nozzles plus data and control circuitry.

Ink is supplied to the back of the printhead by injection molded plastic ink channels. The molding requires 50 micron features, which can be created using a lithographically micromachined insert in a standard injection molding tool. Ink flows through holes etched through the wafer to the nozzle chambers fabricated on the front surface of the wafer. The printhead is connected to the camera circuitry by tape automated bonding.

Tables of Drop-on-Demand Ink Jets

Eleven important characteristics of the fundamental operation of individual ink jet nozzles have been identified. These characteristics are largely orthogonal, and so can be elucidated as an eleven dimensional matrix. Most of the eleven axes of this matrix include entries developed by the present assignee.

The following tables form the axes of an eleven dimensional table of ink jet types.

Actuator mechanism (18 types)

Basic operation mode (7 types)

Auxiliary mechanism (8 types)

Actuator amplification or modification method (17 types)

Actuator motion (19 types)

Nozzle refill method (4 types)

Method of restricting back-flow through inlet (10 types)

Nozzle clearing method (9 types)

Nozzle plate construction (9 types)

Drop ejection direction (5 types)

Ink type (7 types)

The complete eleven dimensional table represented by these axes contains 36.9 billion possible configurations of ink jet nozzle. While not all of the possible combinations result in a viable ink jet technology, many million configurations are viable. It is clearly impractical to elucidate all of the possible configurations. Instead, certain ink jet types have been investigated in detail. These are designated IJ01 to IJ45 which match the docket numbers in the table under the heading Cross References to Related Applications.

Other ink jet configurations can readily be derived from these forty-five examples by substituting alternative configurations along one or more of the 11 axes. Most of the IJ01 to IJ45 examples can be made into ink jet printheads with characteristics superior to any currently available ink jet technology.

Where there are prior art examples known to the inventor, one or more of these examples are listed in the examples column of the tables below. The IJ01 to IJ45 series are also listed in the examples column. In some cases, a print technology may be listed more than once in a table, where it shares characteristics with more than one entry.

Suitable applications for the ink jet technologies include: Home printers, Office network printers, Short run digital printers, Commercial print systems, Fabric printers, Pocket printers, Internet WWW printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.

The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.

Description Advantages Disadvantages Examples ACTUATOR MECHANISM (APPLIED ONLY TO SELECTED INK DROPS) Thermal bubble An electrothermal heater heats Large force generated High power Canon Bubblejet 1979 Endo et the ink to above boiling point, Simple construction Ink carrier limited to water al GB patent 2,0007,162 transferring significant heat to No moving parts Low efficiency Xerox heater-in-pit 1990 the aqueous ink. A bubble Fast operation High temperatures required Hawkins et al U.S. Pat. No. nucleates and quickly forms, Small chip area required for High mechanical stress 4,899,181 expelling the ink. The efficiency actuator Unusual materials required Hewlett-Packard TIJ 1982 of the process is low, with Large drive transistors Vaught et al U.S. Pat. No. typically less than 0.05% of the Cavitation causes actuator 4,490,728 electrical energy being trans- failure formed into kinetic energy of the Kogation reduces bubble drop. formation Large print heads are difficult to fabricate Piezoelectric A piezoelectric crystal such as Low power consumption Very large area required for Kyser et al U.S. Pat. No. lead lanthanum zirconate (PZT) Many ink types can be used actuator 3,946,398 is electrically activated, and Fast operation Difficult to integrate with Zoltan U.S. Pat. No. 3,683,212 either expands, shears, or bends High efficiency electronics 1973 Stemme U.S. Pat. No. to apply pressure to the ink, High voltage drive transistors 3,747,120 ejecting drops. required Epson Stylus Full pagewidth print heads Tektronix impractical due to actuator size IJ04 Requires electrical poling in high field strengths during manufacture Electrostrictive An electric field is used to Low power consumption Low maximum strain (approx. Seiko Epson, Usui et all JP activate electrostriction in Many ink types can be used 0.01%) 253401/96 relaxor materials such as lead Low thermal expansion Large area required for actuator IJ04 lanthanum zirconate titanate Electric field strength due to low strain (PLZT) or lead magnesium required (approx. 3.5 V/μm) Response speed is marginal niobate (PMN). can be generated without (˜10 μs) difficulty High voltage drive transistors Does not require electrical required poling Full pagewidth print heads impractical due to actuator size Ferroelectric An electric field is used to Low power consumption Difficult to integrate with IJ04 induce a phase transition Many ink types can be used electronics between the antiferroelectric Fast operation (<1 μs) Unusual materials such as (AFE) and ferroelectric (FE) Relatively high longitudinal PLZSnT are required phase. Perovskite materials such strain Actuators require a large area as tin modified lead lanthanum High efficiency zirconate titanate (PLZSnT) Electric field strength of around exhibit large strains of up to 1% 3 V/μm can be readily provided associated with the AFE to FE phase transition. Electrostatic Conductive plates are separated Low power consumption Difficult to operate electrostatic IJ02, IJ04 plates by a compressible or fluid Many ink types can be used devices in an aqueous environ- dielectric (usually air). Upon Fast operation ment application of a voltage, the The electrostatic actuator will plates attract each other and normally need to be separated displace ink, causing drop from the ink ejection. The conductive plates Very large area required to may be in a comb or honeycomb achieve high forces structure, or stacked to increase High voltage drive transistors the surface area and therefore may be required the force. Full pagewidth print heads are not competitive due to actuator size Electrostatic A strong electric field is applied Low current consumption High voltage required 1989 Saito et al, U.S. Pat. No. pull on ink to the ink, whereupon electro- Low temperature May be damaged by sparks due 4,799,068 static attraction accelerates the to air breakdown 1989 Miura et al, U.S. Pat. No. ink towards the print medium. Required field strength increases 4,810,954 as the drop size decreases Tone-jet High voltage drive transistors required Electrostatic field attracts dust Permanent An electromagnet directly Low power consumption Complex fabrication IJ07, IJ10 magnet electro- attracts a permanent magnet, Many ink types can be used Permanent magnetic material magnetic displacing ink and causing drop Fast operation such as Neodymium Iron Boron ejection. Rare earth magnets High efficiency (NdFeB) required. with a field strength around 1 Easy extension from single High local currents required Tesla can be used. Examples nozzles to pagewidth print Copper metalization should be are: Samarium Cobalt (SaCo) heads used for long electromigration and magnetic materials in the lifetime and low resistivity neodymium iron boron family Pigmented inks are usually (NdFeB, NdDyFeBNb, infeasible NdDyFeB, etc) Operating temperature limited to the Curie temperature (around 540 K.) Soft magnetic A solenoid induced a magnetic Low power consumption Complex fabrication IJ01, IJ05, IJ08, IJ10, IJ12, IJ14, core electro- field in a soft magnetic core or Many ink types can be used Materials not usually present in IJ15, IJ17 magnetic yoke fabricated from a ferrous Fast operation a CMOS fab such as NiFe, material such as electroplated High efficiency CoNiFe, or CoFe are required iron alloys such as CoNiFe [1], Easy extension from single High local currents required CoFe, or NiFe alloys. Typically, nozzles to pagewidth print Copper metalization should be the soft magnetic material is in heads used for long electromigration two parts, which are normally lifetime and low resistivity held apart by a spring. When the Electroplating is required solenoid is actuated, the two High saturation flux density is parts attract, displacing the ink. required (2.0-2.1 T is achievable with CoNiFe [1]) Lorenz force The Lorenz force acting on a Low power consumption Force acts as a twisting motion IJ06, IJ11, IJ13, IJ16 current carrying wire in a Many ink types can be used Typically, only a quarter of the magnetic field is utilized. This Fast operation solenoid length provides force allows the magnetic field to be High efficiency in a useful direction supplied externally to the print Easy extension from single High local currents required head, for example with rare nozzles to pagewidth print Copper metalization should be earth permanent magnets. Only heads used for long electromigration the current carrying wire need be lifetime and low resistivity fabricated on the print-head, Pigmented inks are usually simplifying materials require- infeasible ments. Magneto- The actuator uses the giant Many ink types can be used Force acts as a twisting motion Fischenbeck, U.S. Pat. No. striction magnetostrictive effect of Fast operation Unusual materials such as 4,032,929 materials such as Terfenol-D (an Easy extension from single Terfenol-D are required IJ25 alloy of terbium, dysprosium nozzles to pagewidth print High local currents required and iron developed at the Naval heads Copper metalization should be Ordnance Laboratory, hence High force is available used for long electromigration Ter-Fe-NOL). For efficiency, lifetime and low resistivity the actuator should be pre- Pre-stressing may be required stressed to approx. 8 MPa. Surface tension Ink under positive pressure is Low power consumption Requires supplementary force Silverbrook, EP 0771 658 A2 reduction held in a nozzle by surface Simple construction to effect drop separation and related patent applications tension. The surface tension of No unusual materials required in Requires special ink surfactants the ink is reduced below the fabrication Speed may be limited by bubble threshold, causing the ink High efficiency surfactant properties to egress from the nozzle. Easy extension from single nozzles to pagewidth print heads Viscosity The ink viscosity is locally Simple construction Requires supplementary force Silverbrook, EP 0771 658 A2 reduction reduced to select which drops No unusual materials required in to effect drop separation and related patent applications are to be ejected. A viscosity fabrication Requires special ink viscosity reduction can be achieved Easy extension from single surfactants electrothermally with most inks, nozzles to pagewidth print High speed is difficult to but special inks can be heads achieve engineered for a 100:1 viscosity Requires oscillating ink pressure reduction. A high temperature difference (typically 80 degrees) is required Acoustic An acoustic wave is generated Can operate without a nozzle Complex drive circuitry 1993 Hadimioglu et al, EUP and focussed upon the drop plate Complex fabrication 550,192 ejection region. Low efficiency 1993 Elrod et al, EUP 572,220 Poor control of drop position Poor control of drop volume Thermoelastic An actuator which relies upon Low power consumption Efficient aqueous operation IJ03, IJ09, IJ17, IJ18, IJ19, IJ20, bend actuator differential thermal expansion Many ink types can be used requires a thermal insulator IJ21, IJ22, IJ23, IJ24, IJ27, IJ28, upon Joule heating is used. Simple planar fabrication on the hot side IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, Small chip area required for Corrosion prevention can be IJ35, IJ36, IJ37, IJ38, IJ39, IJ40, actuator difficult IJ41 Fast operation Pigmented inks may be High efficiency infeasible, as pigment particles CMOS compatible voltages and may jam the bend actuator currents Standard MEMS processes can be used Easy extension from single nozzles to pagewidth print heads High CTE A material with a very high High force can be generated Requires special material (e.g. IJ09, IJ17, IJ18, IJ20, IJ21, IJ22, thermoelastic coefficient of thermal expansion Three methods of PTFE deposi- PTFE) IJ23, IJ24, IJ27, IJ28, IJ29, IJ30, actuator (CTE) such as polytetrafluoro- tion are under development: Requires a PTFE deposition IJ31, IJ42, IJ43, IJ44 ethylene (PTFE) is used. As chemical vapor deposition process, which is not yet high CTE materials are usually (CVD), spin coating, and standard in ULSI fabs non-conductive, a heater fabri- evaporation PTFE deposition cannot be cation from a conductive PTFE is a candidate for low followed with high temper- material is incorporated. A dielectric constant insula- ature (above 350° C.) 50 μm long PTFE bend actuator tion in ULSI processing with polysilicon heater and Very low power consumption Pigmented inks may be 15 mW power input can provide Many ink types can be used infeasible, as pigment particles 180 μN force and 10 μm Simple planar fabrication may jam the bend actuator deflection. Actuator motions Small chip area required for include: actuator Bend Fast operation Push High efficiency Buckle CMOS compatible voltages and Rotate currents Easy extension from single nozzles to pagewidth print heads Conductive A polymer with a high co- High force can be generated Requires special materials IJ24 polymer efficient of thermal expansion Very low power consumption development (High CTE con- thermoelastic (such as PTFE) is doped with Many ink types can be used ductive polymer) conducting substances to Simple planar fabrication Requires a PTFE deposition increase its conductivity to about Small chip area required for process, which is not yet 3 orders of magnitude below that actuator standard in ULSI fabs of copper. The conducting Fast operation PTFE deposition cannot be polymer expands when High efficiency followed with high temper- resistively heated. Examples of CMOS compatible voltages and ature (above 350° C.) conducting dopants include: currents processing Carbon nanotubes Easy extension from single Evaporation and CVD deposi- Metal fibers nozzles to pagewidth print tion techniques cannot be used Conductive polymers such as heads Pigmented inks may be in- doped polythiophene feasible, as pigment particles Carbon granules may jam the bend actuator Shape memory A shape memory alloy such as High force is available Fatigue limits maximum number IJ26 alloy TiNi (also known as Nitinol - (stresses of hundreds of of cycles Nickel Titanium alloy developed MPa) Low strain (1%) is required to at the Naval Ordnance Labora- Large strain is available extend fatigue resistance tory) is thermally switched (more than 3%) Cycle rate limited by heat between its weak martensitic High corrosion resistance removal state and its high stiffness Simple construction Requires unusual materials austenic state. The shape of the Easy extension from single (TiNi) actuator in its martensitic state is nozzles to pagewidth print The latent heat of trans- deformed relative to the austenic heads formation must be provided shape. The shape change causes Low voltage operation High current operation ejection of a drop. Requires pre-stressing to distort the martensitic state Linear Linear magnetic actuators Linear Magnetic actuators can Requires unusual semiconductor IJ12 Magnetic include the Linear Induction be constructed with high thrust, materials such as soft magnetic Actuator Actuator (LIA), Linear long travel, and high efficiency alloys (e.g. CoNiFe) Permanent Magnet Synchronous using planar semiconductor fab- Some varieties also require Actuator (LPMSA), Linear rication techniques permanent magnetic materials Reluctance Synchronous Long actuator travel is available such as Neodymium iron boron Actuator (LRSA), Linear Medium force is available (NdFeB) Switched Reluctance Actuator Low voltage operation Requires complex multiphase (LSRA), and the Linear Stepper drive circuitry Actuator (LSA). High current operation BASIC OPERATION MODE Actuator This is the simplest mode of Simple operation Drop repetition rate is usually Thermal ink jet directly pushes operation: the actuator directly No external fields required limited to around 10 kHz. How- Piezoelectric ink jet ink supplies sufficient kinetic energy Satellite drops can be avoided if ever, this is not fundamental IJ01, IJ02, IJ03, IJ04, IJ05, IJ06, to expel the drop. The drop must drop velocity is less than 4 m/s to the method, but is related IJ07, IJ09, IJ11, IJ12, IJ14, IJ16, have a sufficient velocity to Can be efficient, depending to the refill method normally IJ20, IJ22, IJ23, IJ24, IJ25, IJ26, overcome the surface tension. upon the actuator used used IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, All of the drop kinetic energy IJ33, IJ34, IJ35, IJ36, IJ37, IJ38, must be provided by the actuator IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Satellite drops usually form if drop velocity is greater than 4.5 m/s Proximity The drops to be printed are Very simple print head fabrica- Requires close proximity Silverbrook, EP 0771 658 A2 selected by some manner (e.g. tion can be used between the print head and the and related patent applications thermally induced surface The drop selection means does print media or transfer roller tension reduction of pressurized not need to provide the energy May require two print heads ink). Selected drops are required to separate the drop printing alternate rows of the separated from the ink in the from the nozzle image nozzle by contact with the print Monolithic color print heads are medium or a transfer roller. difficult Electrostatic The drops to be printed are Very simple print head fabri- Requires very high electrostatic Silverbrook, EP 0771 658 A2 pull on ink selected by some manner (e.g. cation can be used field and related patent applications thermally induced surface The drop selection means does Electrostatic field for small Tone-Jet tension reduction of pressurized not need to provide the energy nozzle sizes is above air break- ink). Selected drops are required to separate the drop down separated from the ink in the from the nozzle Electrostatic field may attract nozzle by a strong electric field. dust Magnetic The drops to be printed are Very simple print head fabrica- Requires magnetic ink Silverbrook, EP 0771 658 A2 pull on ink selected by some manner (e.g. tion can be used Ink colors other than black are and related patent applications thermally induced surface The drop selection means does difficult tension reduction of pressurized not need to provide the energy Requires very high magnetic ink). Selected drops are required to separate the drop fields separated from the ink in the from the nozzle nozzle by a strong magnetic field acting on the magnetic ink. Shutter The actuator moves a shutter to High speed (>50 kHz) operation Moving parts are required IJ13, IJ17, IJ21 block ink flow the nozzle. The can be achieved due to reduced Requires ink pressure modulator ink pressure is pulsed at a refill time Friction and wear must be con- multiple of the drop ejection Drop timing can be very sidered frequency. accurate Stiction is possible The actuator energy can be very low Shuttered The actuator moves a shutter to Actuators with small travel can Moving parts are required IJ08, IJ15, IJ18, IJ19 grill block ink flow through a grill to be used Requires ink pressure modulator the nozzle. The shutter move- Actuators with small force can Friction and wear must be con- ment need only be equal to the be used sidered width of the grill holes. High speed (>50 kHz) operation Stiction is possible can be achieved Pulsed mag- A pulsed magnetic field attracts Extremely low energy operation Requires an external pulsed IJ10 netic pull on an ‘ink pusher’ at the drop is possible magnetic field ink pusher ejection frequency. An actuator No heat dissipation problems Requires special materials for controls a catch, which prevents both the actuator and the ink the ink pusher from moving pusher when a drop is not to be ejected. Complex construction AUXILIARY MECHANISM (APPLIED TO ALL NOZZLES) None The actuator directly fires the Simplicity of construction Drop ejection energy must be Most ink jets, including piezo- ink drop, and there is no external Simplicity of operation supplied by individual nozzle electric and thermal bubble. field or other mechanism Small physical size actuator IJ01, IJ02, IJ03, IJ04, IJ05, IJ07, required. IJ09, IJ11, IJ12, IJ14, IJ20, IJ22, IJ23, IJ24, IJ25, IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Oscillating ink The ink pressure oscillates, pro- Oscillating ink pressure can Requires external ink pressure Silverbrook, EP 0771 658 A2 pressure viding much of the drop ejection provide a refill pulse, allowing oscillator and related patent applications (including energy. The actuator selects higher operating speed Ink pressure phase and IJ08, IJ13, IJ15, IJ17, IJ18, IJ19, acoustic which drops are to be fired by The actuators may operate with amplitude must be carefully IJ21 stimulation) selectively blocking or enabling much lower energy controlled nozzles. The ink pressure Acoustic lenses can be used to Acoustic reflections in the ink oscillation may be achieved by focus the sound on the nozzles chamber must be designed for vibrating the print head, or preferably by an actuator in the ink supply. Media The print head is placed in close Low power Precision assembly required Silverbrook, EP 0771 658 A2 proximity proximity to the print medium. High accuracy Paper fibers may cause problems and related patent applications Selected drops protrude from the Simple print head construction Cannot print on rough substrates print head further than unselected drops, and contact the print medium. The drop soaks into the medium fast enough to cause drop separation. Transfer roller Drops are printed to a transfer High accuracy Bulky Silverbrook, EP 0771 658 A2 roller instead of straight to the Wide range of print substrates Expensive and related patent applications print medium. A transfer roller can be used Complex construction Tektronix hot melt piezoelectric can also be used for proximity Ink can be dried on the transfer ink jet drop separation. roller Any of the IJ series Electrostatic An electric field is used to Low power Field strength required for Silverbrook, EP 0771 658 A2 accelerate selected drops Simple print head construction separation of small drops is near and related patent applications towards the print medium. or above air breakdown Tone-Jet Direct mag- A magnetic field is used to Low power Requires magnetic ink Silverbrook, EP 0771 658 A2 netic field accelerate selected drops of Simple print head construction Requires strong magnetic field and related patent applications magnetic ink towards the print medium. Cross magnetic The print head is placed in a Does not require magnetic Requires external magnet IJ06, IJ16 field constant magnetic field. The materials to be integrated in the Current densities may be high, Lorenz force in a current carry- print head manufacturing resulting in electromigration ing wire is used to move the process problems actuator. Pulsed mag- A pulsed magnetic field is used Very low power operation is Complex print head construction IJ10 netic field to cyclically attract a paddle, possible Magnetic materials required in which pushes on the ink. A Small print head size print head small actuator moves a catch, which selectively prevents the paddle from moving. ACTUATOR AMPLIFICATION OR MODIFICATION METHOD None No actuator mechanical amplifi- Operational simplicity Many actuator mechanisms have Thermal Bubble Ink jet cation is used. The actuator insufficient travel, or insufficient IJ01, IJ02, IJ06, IJ07, IJ16, IJ25, directly drives the drop ejection force, to efficiently drive the IJ26 process. drop ejection process Differential An actuator material expands Provides greater travel in a High stresses are involved Piezoelectric expansion more on one side than on the reduced print head area Care must be taken that the IJ03, IJ09, IJ17, IJ18, IJ19, IJ20, bend actuator other. The expansion may be materials do not delaminate IJ21, IJ22, IJ23, IJ24, IJ27, IJ29, thermal, piezoelectric, magneto- Residual bend resulting from IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, strictive, or other mechanism. high temperature or high stress IJ36, IJ37, IJ38, IJ39, IJ42, IJ43, The bend actuator converts a during formation IJ44 high force low travel actuator mechanism to high travel, lower force mechanism. Transient bend A trilayer bend actuator where Very good temperature stability High stresses are involved IJ40, IJ41 actuator the two outside layers are High speed, as a new drop can Care must be taken that the identical. This cancels bend due be fired before heat dissipates materials do not delaminate to ambient temperature and Cancels residual stress of residual stress. The actuator only formation responds to transient heating of one side or the other. Reverse spring The actuator loads a spring. Better coupling to the ink Fabrication complexity IJ05, IJ11 When the actuator is turned off, High stress in the spring the spring releases. This can reverse the force/distance curve of the actuator to make it compatible with the force/time requirements of the drop ejection. Actuator stack A series of thin actuators are Increased travel Increased fabrication complexity Some piezoelectric ink jets stacked. This can be appropriate Reduced drive voltage Increased possibility of short IJ04 where actuators require high circuits due to pinholes electric field strength, such as electrostatic and piezoelectric actuators. Multiple Multiple smaller actuators are Increases the force available Actuator forces may not added IJ12, IJ13, IJ18, IJ20, IJ22, IJ28, actuators used simultaneously to move the from an actuator linearly, reducing efficiency IJ42, IJ43 ink. Each actuator need provide Multiple actuators can be only a portion of the force positioned to control ink flow accurately required. Linear Spring A linear spring is used to Matches low travel actuator with Requires print head area for the IJ15 transform a motion with small higher travel requirements spring travel and high force into a Non-contact method of motion longer travel, lower force transformation motion. Coiled actuator A bend actuator is coiled to Increased travel Generally restricted to planar IJ17, IJ21, IJ34, IJ35 provide greater travel in a Reduced chip area implementations due to extreme reduced chip area. Planar implementations are fabrication difficulty in other relatively easy to fabricate. orientations. Flexure bend A bend actuator has a small Simple means of increasing Care must be taken not to IJ10, IJ19, IJ33 actuator region near the fixture point, travel of a bend actuator exceed the elastic limit in the which flexes much more readily flexure area than the remainder of the Stress distribution is very actuator. The actuator flexing is uneven effectively converted from an Difficult to accurately model even coiling to an angular bend, with finite element analysis resulting in greater travel of the actuator tip. Catch The actuator controls a small Very low actuator energy Complex construction IJ10 catch. The catch either enables Very small actuator size Requires external force or disables movement of an ink Unsuitable for pigmented inks pusher that is controlled in a bulk manner. Gears Gears can be used to increase Low force, low travel actuators Moving parts are required IJ13 travel at the expense of duration. can be used Several actuator cycles are Circular gears, rack and pinion, Can be fabricated using standard required ratchets, and other gearing surface MEMS processes More complex drive electronics methods can be used. Complex construction Friction, friction, and wear are possible Buckle plate A buckle plate can be used to Very fast movement achievable Must stay within elastic limits of S. Hirata et al, “An Ink-jet Head change a slow actuator into a the materials for long device life Using Diaphragm Micro- fast motion. It can also convert High stresses involved actuator”, Proc. IEEE MEMS, a high force, low travel actuator Generally high power require- Feb. 1996, pp 418-423. into a high travel, medium force ment IJ18, IJ27 motion. Tapered mag- A tapered magnetic pole can Linearizes the magnetic force/ Complex construction IJ14 netic pole increase travel at the expense of distance curve force. Lever A lever and fulcrum is used to Matches low travel actuator with High stress around the fulcrum IJ32, IJ36, IJ37 transform a motion with small higher travel requirements travel and high force into a Fulcrum area has no linear motion with longer travel and movement, and can be used for a lower force. The lever can also fluid seal reverse the direction of travel. Rotary The actuator is connected to a High mechanical advantage Complex construction IJ28 impeller rotary impeller. A small angular The ratio of force to travel of Unsuitable for pigmented inks deflection of the actuator results the actuator can be matched to in a rotation of the impeller the nozzle requirements by vanes, which push the ink varying the number of impeller against stationary vanes and out vanes of the nozzle. Acoustic lens A refractive or diffractive (e.g. A moving parts Large area required 1993 Hadimioglu et al, EUP zone plate) acoustic lens is used Only relevant for acoustic ink 550,192 to concentrate sound waves. jets 1993 Elrod et al, EUP 572,220 Sharp conduc- A sharp point is used to con- Simple construction Difficult to fabricate using Tone-jet tive point centrate an electrostatic field. standard VLSI processes for a surface ejecting ink-jet Only relevant for electrostatic ink jets ACTUATOR MOTION Volume expan- The volume of the actuator Simple construction in the case High energy is typically required Hewlett-Packard Thermal Ink jet sion changes, pushing the ink in all of thermal ink jet to achieve volume expansion. Canon Bubblejet directions. This leads to thermal stress, cavitation, and kogation in thermal ink jet implementations Linear, normal The actuator moves in a Efficient coupling to ink drops High fabrication complexity may IJ01, IJ02, IJ04, IJ07, IJ11, IJ14 to chip surface direction normal to the print ejected normal to the surface be required to achieve per- head surface. The nozzle is pendicular motion typically in the line of movement. Parallel to The actuator moves parallel to Suitable for planar fabrication Fabrication complexity IJ12, IJ13, IJ15, IJ33, IJ34, IJ35, chip surface the print head surface. Drop Friction IJ36 ejection may still be normal to Stiction the surface. Membrane An actuator with a high force The effective area of the actuator Fabrication complexity 1982 Howkins U.S. Pat. No. push but small area is used to push a becomes the membrane area Actuator size 4,459,601 stiff membrane that is in contact Difficulty of integration in a with the ink. VLSI process Rotary The actuator causes the rotation Rotary levers may be used to Device complexity IJ05, IJ08, IJ13, IJ28 of some element, such a grill or increase travel May have friction at a pivot impeller Small chip area requirements point Bend The actuator bends when A very small change in Requires the actuator to be made 1970 Kyser et al U.S. Pat. No. energized. This may be due to dimensions can be converted to from at least two distinct layers, 3,946,398 differential thermal expansion, a large motion. or to have a thermal difference 1973 Stemme U.S. Pat. No. piezoelectric expansion, across the actuator 3,747,120 magnetostriction, or other form IJ03, IJ09, IJ10, IJ19, IJ23, IJ24, of relative dimensional change. IJ25, IJ29, IJ30, IJ31, IJ33, IJ34, IJ35 Swivel The actuator swivels around a Allows operation where the net Inefficient coupling to the ink IJ06 central pivot. The motion is linear force on the paddle is zero motion suitable where there are opposite Small chip area requirements forces applied to opposite sides of the paddle, e.g. Lorenz force. Straighten The actuator is normally bent, Can be used with shape memory Requires careful balance of IJ26, IJ32 and straightens when energized. alloys where the austenic phase stresses to ensure that the is planar quiescent bend is accurate Double bend The actuator bends in one One actuator can be used to Difficult to make the drops IJ36, IJ37, IJ38 direction when one element is power two nozzles. ejected by both bend directions energized, and bends the other Reduced chip size. identical. way when another element is Not sensitive to ambient A small efficiency loss energized. temperature compared to equivalent single bend actuators. Shear Energizing the actuator causes a Can increase the effective travel Not readily applicable to other 1985 Fishbeck U.S. Pat. No. shear motion in the actuator of piezoelectric actuators actuator mechanisms 4,584,590 material. Radial con- The actuator squeezes an ink Relatively easy to fabricate High force required 1970 Zoltan U.S. Pat. No. striction reservoir, forcing ink from a single nozzles from glass tubing Inefficient 3,683,212 constricted nozzle. as macroscopic structures Difficult to integrate with VLSI processes Coil/uncoil A coiled actuator uncoils or coils Easy to fabricate as a planar Difficult to fabricate for non- IJ17, IJ21, IJ34, IJ35 more tightly. The motion of the VLSI process planar devices free end of the actuator ejects Small area required, therefore Poor out-of-plane stiffness the ink. low cost Bow The actuator bows (or buckles) Can increase the speed of travel Maximum travel is constrained IJ16, IJ18, IJ27 in the middle when energized. Mechanically rigid High force required Push-Pull Two actuators control a shutter. The structure is pinned at both Not readily suitable for ink jets IJ18 One actuator pulls the shutter, ends, so has a high out-of-plane which directly push the ink and the other pushes it. rigidity Curl inwards A set of actuators curl inwards Good fluid flow to the region Design complexity IJ20, IJ42 to reduce the volume of ink that behind the actuator increases they enclose. efficiency Curl outwards A set of actuators curl outwards, Relatively simple construction Relatively large chip area IJ43 pressurizing ink in a chamber surrounding the actuators, and expelling ink from a nozzle in the chamber. Iris Multiple vanes enclose a volume High efficiency High fabrication complexity IJ22 of ink. These simultaneously Small chip area Not suitable for pigmented inks rotate, reducing the volume between the vanes. Acoustic The actuator vibrates at a high The actuator can be physically Large area required for efficient 1993 Hadimioglu et al, EUP vibration frequency. distant from the ink operation at useful frequencies 550,192 Acoustic coupling and crosstalk 1993 Elrod et al, EUP 572,220 Complex drive circuitry Poor control of drop volume and position None In various ink jet designs the No moving parts Various other tradeoffs are Silverbrook, EP 0771 658 A2 actuator does not move. required to eliminate moving and related patent applications parts Tone-jet NOZZLE REFILL METHOD Surface tension This is the normal way that ink Fabrication simplicity Low speed Thermal ink jet jets are refilled. After the Operational simplicity Surface tension force relatively Piezoelectric ink jet actuator is energized, it typically small compared to actuator force IJ01-IJ07, IJ10-IJ14, IJ16, IJ20, returns rapidly to its normal Long refill time usually IJ22-IJ45 position. This rapid return sucks dominates the total repetition in air through the nozzle rate opening. The ink surface tension at the nozzle then exerts a small force restoring the meniscus to a minimum area. This force refills the nozzle. Shuttered Ink to the nozzle chamber is High speed Requires common ink pressure IJ08, IJ13, IJ15, IJ17, IJ18, IJ19, oscillating provided at a pressure that Low actuator energy, as the oscillator IJ21 ink pressure oscillates at twice the drop actuator need only open or close May not be suitable for ejection frequency. When a drop the shutter, instead of ejecting pigmented inks is to be ejected, the shutter is the ink drop opened for 3 half cycles: drop ejection, actuator return, and refill. The shutter is then closed to prevent the nozzle chamber emptying during the next negative pressure cycle. Refill actuator After the main actuator has High speed, as the nozzle is Requires two independent IJ09 ejected a drop a second (refill) actively refilled actuators per nozzle actuator is energized. The refill actuator pushes ink into the nozzle chamber. The refill actuator returns slowly, to prevent its return from emptying the chamber again. Positive ink The ink is held a slight positive High refill rate, therefore a high Surface spill must be prevented Silverbrook, EP 0771 658 A2 pressure pressure. After the ink drop is drop repetition rate is possible Highly hydrophobic print head and related patent applications ejected, the nozzle chamber fills surfaces are required Alternate for: IJ01-IJ07, IJ10- quickly as surface tension and IJ14, IJ16, IJ20, IJ22-IJ45 ink pressure both operate to refill the nozzle. METHOD OF RESTRICTING BACK-FLOW THROUGH INLET Long inlet The ink inlet channel to the Design simplicity Restricts refill rate Thermal ink jet channel nozzle chamber is made long Operational simplicity May result in a relatively large Piezoelectric ink jet and relatively narrow, relying on Reduces crosstalk chip area IJ42, IJ43 viscous drag to reduce inlet Only partially effective back-flow Positive ink The ink is under a positive Drop selection and separation Requires a method (such as a Silverbrook, EP 0771 658 A2 pressure pressure, so that in the quiescent forces can be reduced nozzle rim or effective hydro- and related patent applications state some of the ink drop Fast refill time phobizing, or both) to prevent Possible operation of the already protrudes from the flooding of the ejection surface following: IJ01-IJ07, IJ09-IJ12, nozzle. This reduces the pressure of the print head. IJ14, IJ16, IJ20, IJ22, IJ23-IJ34, in the nozzle chamber which is IJ36-IJ41, IJ44 required to eject a certain volume of ink. The reduction in chamber pressure results in a reduction in ink pushed out through the inlet. Baffle One or more baffles are placed The refill rate is not as restricted Design complexity HP Thermal Ink Jet in the inlet ink flow. When the as the long inlet method. May increase fabrication Tektronix piezoelectric ink jet actuator is energized, the rapid Reduces crosstalk complexity (e.g. Tektronix hot ink movement creates eddies melt Piezoelectric print heads). which restrict the flow through the inlet. The slower refill process is unrestricted, and does not result in eddies. Flexible flap In this method recently disclosed Significantly reduces back-flow Not applicable to most ink jet Canon restricts inlet by Canon, the expanding for edge-shooter thermal ink jet configurations actuator (bubble) pushes on a devices Increased fabrication complexity flexible flap that restricts the Inelastic deformation of polymer inlet. flap results in creep over extended use Inlet filter A filter is located between the Additional advantage of ink Restricts refill rate IJ04, IJ12, IJ24, IJ27, IJ29, IJ30 ink inlet and the nozzle filtration May result in complex chamber. The filter has a Ink filter may be fabricated with construction multitude of small holes or slots, no additional process steps restricting ink flow. The filter also removes particles which may block the nozzle. Small inlet The ink inlet channel to the Design simplicity Restricts refill rate IJ02, IJ37, IJ44 compared to nozzle chamber has a sub- May result in a relatively large nozzle stantially smaller cross section chip area than that of the nozzle, resulting Only partially effective in easier ink egress out of the nozzle than out of the inlet. Inlet shutter A secondary actuator controls Increases speed of the ink-jet Requires separate refill actuator IJ09 the position of a shutter, closing print head operation and drive circuit off the ink inlet when the main actuator is energized. The inlet is The method avoids the problem Back-flow problem is eliminated Requires careful design to IJ01, IJ03, IJ05, IJ06, IJ07, IJ10, located behind of inlet back-flow by arranging minimize the negative pressure IJ11, IJ14, IJ16, IJ22, IJ23, IJ25, the ink-pushing the ink-pushing surface of the behind the paddle IJ28, IJ31, IJ32, IJ33, IJ34, IJ35, surface actuator between the inlet and IJ36, IJ39, IJ40, IJ41 the nozzle. Part of the The actuator and a wall of the Significant reductions in back- Small increase in fabrication IJ07, IJ20, IJ26, IJ38 actuator moves ink chamber are arranged so that flow can be achieved complexity to shut off the the motion of the actuator closes Compact designs possible inlet off the inlet. Nozzle actuator In some configurations of ink Ink back-flow problem is None related to ink back-flow on Silverbrook, EP 0771 658 A2 does not result jet, there is no expansion or eliminated actuation and related patent applications in ink back- movement of an actuator which Valve-jet flow may cause ink back-flow Tone-jet through the inlet. NOZZLE CLEARING METHOD Normal nozzle All of the nozzles are fired No added complexity on the May not be sufficient to displace Most ink jet systems firing periodically, before the ink has a print head dried ink IJ01, IJ02, IJ03, IJ04, IJ05, IJ06, chance to dry. When not in use IJ07, IJ09, IJ10, IJ11, IJ12, IJ14, the nozzles are sealed (capped) IJ16, IJ20, IJ22, IJ23, IJ24, IJ25, against air. The nozzle firing is IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, usually performed during a IJ32, IJ33, IJ34, IJ36, IJ37, IJ38, special clearing cycle, after first IJ39, IJ40, IJ41, IJ42, IJ43, IJ44, moving the print head to a IJ45 cleaning station. Extra power In systems which heat the ink, Can be highly effective if the Requires higher drive voltage Silverbrook, EP 0771 658 A2 to ink heater but do not boil it under normal heater is adjacent to the nozzle for clearing and related patent applications situations, nozzle clearing can be May require larger drive achieved by over-powering the transistors heater and boiling ink at the nozzle. Rapid success- The actuator is fired in rapid Does not require extra drive Effectiveness depends sub- May be used with: IJ01, IJ02, ion of actuator succession. In some configura- circuits on the print head stantially upon the configuration IJ03, IJ04, IJ05, IJ06, IJ07, IJ09, pulses tions, this may cause heat build- Can be readily controlled and of the ink jet nozzle IJ10, IJ11, IJ14, IJ16, IJ20, IJ22, up at the nozzle which boils the initiated by digital logic IJ23, IJ24, IJ25, IJ27, IJ28, IJ29, ink, clearing the nozzle. In other IJ30, IJ31, IJ32, IJ33, IJ34, IJ36, situations, it may cause IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, sufficient vibrations to dislodge IJ43, IJ44, IJ45 clogged nozzles. Extra power to Where an actuator is not A simple solution where Not suitable where there is a May be used with: IJ03, IJ09, ink pushing normally driven to the limit of applicable hard limit to actuator movement IJ16, IJ20, IJ23, IJ24, IJ25, IJ27, actuator its motion, nozzle clearing may IJ29, IJ30, IJ31, IJ32, IJ39, IJ40, be assisted by providing an IJ41, IJ42, IJ43, IJ44, IJ45 enhanced drive signal to the actuator. Acoustic An ultrasonic wave is applied to A high nozzle clearing capability High implementation cost if IJ08, IJ13, IJ15, IJ17, IJ18, IJ19, resonance the ink chamber. This wave is of can be achieved system does not already include IJ21 an appropriate amplitude and May be implemented at very low an acoustic actuator frequency to cause sufficient cost in systems which already force at the nozzle to clear include acoustic actuators blockages. This is easiest to achieve if the ultrasonic wave is at a resonant frequency of the ink cavity. Nozzle clearing A microfabricated plate is Can clear severely clogged Silverbrook, EP 0771 658 A2 plate pushed against the nozzles. The nozzles and related patent applications plate has a post for every nozzle. Moving parts are required A post moves through each There is risk of damage to the nozzle, displacing dried ink. nozzles Accurate fabrication is required Ink pressure The pressure of the ink is May be effective where other Requires pressure pump or other May be used with all IJ series pulse temporarily increased so that methods cannot be used pressure actuator ink jets ink streams from all of the Expensive nozzles. This may be used in Wasteful of ink conjunction with actuator energizing. Print head A flexible ‘blade’ is wiped Effective for planar print head Difficult to use if print head Many ink jet systems wiper across the print head surface. surfaces surface is non-planar or very The blade is usually fabricated Low cost fragile from a flexible polymer, e.g. Requires mechanical parts rubber or synthetic elastomer. Blade can wear out in high volume print systems Separate ink A separate heater is provided at Can be effective where other Fabrication complexity Can be used with many IJ series boiling heater the nozzle although the normal nozzle clearing methods cannot ink jets drop e-ection mechanism does be used not require it. The heaters do not Can be implemented at no require individual drive circuits, additional cost in some ink jet as many nozzles can be cleared configurations simultaneously, and no imaging is required. NOZZLE PLATE CONSTRUCTION Electroformed A nozzle plate is separately Fabrication simplicity High temperatures and pressures Hewlett Packard Thermal Ink jet nickel fabricated from electroformed are required to bond nozzle plate nickel, and bonded to the print Minimum thickness constraints head chip. Differential thermal expansion Laser ablated Individual nozzle holes are No masks required Each hole must be individually Canon Bubblejet or drilled ablated by an intense UV laser Can be quite fast formed 1988 Sercel et al., SPIE, Vol. polymer in a nozzle plate, which is Some control over nozzle profile Special equipment required 998 Excimer Beam Applica- typically a polymer such as is possible Slow where there are many tions, pp. 76-83 polyimide or polysulphone Equipment required is relatively thousands of nozzles per print 1993 Watanabe et al., U.S. Pat. low cost head No. 5,208,604 May produce thin burrs at exit holes Silicon micro- A separate nozzle plate is micro- High accuracy is attainable Two part construction K. Bean, IEEE Transactions machined machined from single crystal High cost on Electron Devices, Vol. silicon, and bonded to the print Requires precision alignment ED-25, No. 10, 1978, pp 1185- head wafer. Nozzles may be clogged by 1195 adhesive Xerox 1990 Hawkins et al., U.S. Pat. No. 4,899,181 Glass Fine glass capillaries are drawn No expensive equipment Very small nozzle sizes are 1970 Zoltan U.S. Pat. No. capillaries from glass tubing. This method required difficult to form 3,683,212 has been used for making Simple to make single nozzles Not suited for mass production individual nozzles, but is difficult to use for bulk manufacturing of print heads with thousands of nozzles. Monolithic, The nozzle plate is deposited High accuracy (<1 μm) Requires sacrificial layer under Silverbrook, EP 0771 658 A2 surface micro- as a layer using standard VLSI Monolithic the nozzle plate to form the and related patent applications machined using deposition techniques. Nozzles Low cost nozzle plate to form the IJ01, IJ02, IJ04, IJ11, IJ12, IJ17, VLSI litho- are etched in the nozzle plate Existing processes can be used nozzle chamber IJ18, IJ20, IJ22, IJ24, IJ27, IJ28, graphic pro- using VLSI lithography and Surface may be fragile to the IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, cesses etching. touch IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Monolithic, The nozzle plate is a buried High accuracy (<1 μm) Requires long etch times IJ03, IJ05, IJ06, IJ07, IJ08, IJ09, etched through etch stop in the wafer. Nozzle Monolithic Requires a support wafer IJ10, IJ13, IJ14, IJ15, IJ16, IJ19, substrate chambers are etched in the Low cost IJ21, IJ23, IJ25, IJ26 front of the wafer, and the No differential expansion wafer is thinned from the back side. Nozzles are then etched in the etch stop layer. No nozzle plate Various methods have been tried No nozzles to become clogged Difficult to control drop position Ricoh 1995 Sekiya et al U.S. to eliminate the nozzles entirely, accurately Pat. No. 5,412,413 to prevent nozzle clogging. Crosstalk problems 1993 Hadimioglu et al EUP These include thermal bubble 550,192 mechanisms and acoustic lens 1993 Elrod et al EUP 572,220 mechanisms Trough Each drop ejector has a trough Reduced manufacturing Drop firing direction is IJ35 through which a paddle moves. complexity sensitive to wicking. There is no nozzle plate. Monolithic Nozzle slit The elimination of nozzle holes No nozzles to become clogged Difficult to control drop 1989 Saito et al U.S. Pat. No. instead of and replacement by a slit position accurately 4,799,068 individual encompassing many actuator Crosstalk problems nozzles positions reduces nozzle clogging, but increases cross- talk due to ink surface waves DROP EJECTION DIRECTION Edge (‘edge Ink flow is along the surface Simple construction Nozzles limited to edge Canon Bubblejet 1979 Endo shooter’) of the chip, and ink drops are No silicon etching required High resolution is difficult et al GB patent 2,007,162 ejected from the chip edge. Good heat sinking via substrate Fast color printing requires Xerox heater-in-pit 1990 Mechanically strong one print head per color Hawkins et al U.S. Pat. No. Ease of chip handling 4,899,181 Tone-jet Surface (‘roof Ink flow is along the surface No bulk silicon etching required Maximum ink flow is severely Hewlett-Packard TIJ 1982 shooter’) of the chip, and ink drops are Silicon can make an effective restricted Vaught et al U.S. Pat. No. ejected from the chip surface, heat sink 4,490,728 normal to the plane of the chip. Mechanical strength IJ02, IJ11, IJ12, IJ20, IJ22 Through chip, Ink flow is through the chip, and High ink flow Requires bulking silicon etching Silverbrook, EP 0771 658 A2 forward (‘up ink drops are ejected from the Suitable for pagewidth print and related patent applications shooter’) front surface of the chip. heads IJ04, IJ17, IJ18, IJ24, IJ27-IJ25 High nozzle packing density therefore low manufacturing cost Through chip, Ink flow is through the chip, and High ink flow Requires wafer thinning IJ01, IJ03, IJ05, IJ06, IJ07, IJ08, reverse (‘down ink drops are ejected from the Suitable for pagewidth print Requires special handling during IJ09, IJ10, IJ13, IJ14, IJ15, IJ16, shooter’) rear surface of the chip. heads manufacture IJ19, IJ21, IJ23, IJ25, IJ26 High nozzle packing density therefore low manufacturing cost Through Ink flow is through the actuator, Suitable for piezoelectric print Pagewidth print heads require Epson Stylus which is not fabricated as part of heads several thousand connections to Tektronix hot melt piezoelectric the same substrate as the drive drive circuits ink jets transistors. Cannot be manufactured in standard CMOS fabs Complex assembly required INK TYPE Aqueous, dye Water based ink which typically Environmentally friendly Slow drying Most existing ink jets contains: water, dye, surfactant, No odor Corrosive All IJ series ink jets humectant, and biocide. Modern Bleeds on paper Silverbrook, EP 0771 658 A2 ink dyes have high water- May strikethrough and related patent applications fastness, light fastness Cockles paper Aqueous, Water based ink which typically Environmentally friendly Slow drying IJ02, IJ04, IJ21, IJ26, IJ27, IJ30 pigment contains: water, pigment, No odor Corrosive Silverbrook, EP 0771 658 A2 surfactant, humectant, and Reduced bleed Pigment may clog nozzles and related patent applications biocide. Pigments have an Reduced wicking Pigment may clog actuator Piezoelectric ink-jets advantage in reduced bleed, Reduced strikethrough mechanisms Thermal ink jets (with signifi- wicking and strikethrough. Cockles paper cant restrictions) Methyl Ethyl MEK is a highly volatile solvent Very fast drying Odorous All IJ series ink jets Ketone (MEK) used for industrial printing on Prints on various substrates Flammable difficult surfaces such as such as metals and plastics aluminum cans. Alcohol Alcohol based inks can be used Fast drying Slight odor All IJ series ink jets (ethanol, 2- where the printer must operate Operates at sub-freezing temper- Flammable butanol, and at temperatures below the atures others) freezing point of water. An Reduced paper cockle example of this is in-camera Low cost consumer photographic printing. Phase change The ink is solid at room temper- No drying time-ink instantly High viscosity Tektronix hot melt piezoelectric (hot melt) ature, and is melted in the print freezes on the print medium Printed ink typically has a ink jets head before jetting. Hot melt Almost any print medium can be ‘waxy’ feel 1989 Nowak U.S. Pat. No. inks are usually wax based, with used Printed pages may ‘block’ 4,820,346 a melting point around 80° C.. No paper cockle occurs Ink temperature may be above All IJ series ink jets After jetting the ink freezes No wicking occurs the curie point of permanent almost instantly upon contacting No bleed occurs magnets the print medium or a transfer No strikethrough occurs Ink heaters consume power roller. Long warm-up time Oil Oil based inks are extensively High solubility medium for High viscosity: this is a signifi- All IJ series ink jets used in offset printing. They some dyes cant limitation for use in ink have advantages in improved Does not cockle paper jets, which usually require a low characteristics on paper Does not wick through paper viscosity. Some short chain and (especially no wicking or multi-branched oils have a cockle). Oil soluble dies and sufficiently low viscosity. pigments are required. Slow drying Microemulsion A microemulsion is a stable, Stops ink bleed Viscosity higher than water All IJ series ink jets self forming emulsion of oil, High dye solubility Cost is slightly higher than water water, and surfactant. The Water, oil, and amphiphilic based ink characteristic drop size is less soluble dies can be used High surfactant concentration than 100 nm, and is determined Can stabilize pigment required (around 5%) by the preferred curvature of the suspensions surfactant. 

We claim:
 1. A method of fabricating an ink jet print head, the method including the steps of: depositing a layer of a hydrophobic material on a wafer incorporating drive circuitry and etching the hydrophobic material to define air inlets in the layer of hydrophobic material; forming a plurality of thermal actuators, by deposition and etching techniques, on the layer of hydrophobic material so that each thermal actuator comprises at least a conductive heating portion positioned within hydrophobic material and spaced from the layer of hydrophobic material deposited on the wafer, the thermal actuators being formed so that the air inlets are in fluid communication with a surface of each thermal actuator; and forming a plurality of nozzle chambers on the wafer, by deposition and etching of a sacrificial material so that each thermal actuator is positioned within a nozzle chamber, and so that each nozzle chamber has an ink ejection port.
 2. A method as claimed in claim 1, wherein the layer of hydrophobic material deposited on the wafer is etched so that the layer of hydrophobic material and the wafer define an air inlet channel in fluid communication with a plurality of holes positioned adjacent each thermal actuator. 